(453f) Understanding the Influence of Carbon Dioxide on the Adsorption of Butanol from the Off-Gas from the ABE Fermentation

The production of bio-alcohols has gained immense interest as an alternative to petroleum-based fuels, as a result of increasing fossil fuel prices and environmental issues. Among bio-alcohols, bio-butanol has shown superior properties such as higher energy and lower volatility and water miscibility. [1] However, the economical production of bio-butanol remains a major challenge as the fermentation production of butanol, ABE (acetone/butanol/ethanol) fermentation, produces a mixture of the three components diluted in water. In the recent years, adsorption on molecular sieves has been posted as the cheapest and most energy-efficient technique for the recovery of butanol from fermentation broth. It is for this reason that many studies have been developed on this regard using activated carbons, zeolites, and Metal-Organic Frameworks (MOFs). [2, 3, 4] Most studies focus on the separation of the main mixture from water. However, other gases such as hydrogen or carbon dioxide are produced as well during the process. Carbon dioxide is responsible for the increment of the amount of butanol present at the head space of the fermentation chamber, however not many studies deal with this phase. Working with the vapor phase has some advantages such as preventing clogging of the adsorbents or the influence of pH. This paper studies the effect of the presence of carbon dioxide on the adsorption of butanol at a molecular level. With this aim in mind, competitive adsorption isotherms and multicomponent vapor phase (water/ABE) breakthrough curves were determined on two zeolitic materials (CHA and LTA) and on a hydrophobic metal-organic framework ZIF-8 in absence and presence of CO₂. In a computational section, Monte Carlo simulations and Molecular Dynamics were employed to study the adsorption and diffusion of binary mixtures containing carbon dioxide and butanol. Prior to the analysis of the mixtures, a model for butanol that reproduces experimental properties of the molecule such as its polarity and vapor-liquid coexistence has been developed. Pure component isotherms and heats of adsorption have been computed and compared to experimental data to check the accuracy of the interacting parameters. Finally, to get a better understanding of the molecular mechanism that governs the adsorption of the targeted mixture (CO₂/butanol) in the selected materials we also analyze the distribution of the molecules inside the structures. A combination of these features together with the computation of self-diffusion coefficients allow us to get a global picture of the process and to identify the role of carbon dioxide in the butanol purification process.

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[2] Cao, Y., Wang, K., Wang, X., Gu, Z., Gibbons, W., and Vu, H., App. Surf. Sci. 349

(2015) 1-7.

[3] Cousin Saint Remi, J., Baron, G., and Denayer, J. Adsorption. 18 (2012) 367-373.

[4] Cousin Saint Remi, J., Remy, T., Van Hunskerken, V., van der Perre S., Duerinck, T.,

Maes, M., De Vos, D., Gobechiya, E., Kirshhock, C. E. A., Baron, G. V., and Denayer, J.

F. M., ChemSusChem. 4 (2011) 1074-1077.